1. Field of the Invention
The present invention relates to a multi-layered substrate manufacture and more particularly to a design of built-in capacitors in flip-chip build-up substrate and in BGA substrate.
2. Description of the Prior Art
Recently, with the advent of the microelectronic devices, the trend of device design is demanded to scale down not only to the active-devices, such as transistors but also to the passive-devices, such as resistors in order to increase the integral per unit chip and make the cost down. The design of the printed circuit board (PCB) used to mount the IC chip and the interconnection thereof have become a trend of forming the multi-layered PCB as well. In general, a basic PCB is formed of a dielectric layer and a conductive layer, which has connection thereon. A multi-layered PCB means several of basic PCB boards assembled sequentially together. The top layer provides ICs and other electronic devices (e.g. resistors, capacitors and varieties connectors) supporting and the underlying layers embedded with interconnection circuits. The interconnection between layer to layer is through the plated through holes or vias.
Referring to FIG. 1, for the purpose of alleviating the interference during the signal transferring, the signal plane 10, the power plane 20 and ground plane 30 on the multi-layered substrate are usually designed individually. The signal planes are conductive trace layers mounting on a dielectric layer 15 and 25; for instance, the BT glass fiber, FR4, or the epoxy dielectric layer. However, one of the problems associated with the use of multi-layered substrate is the voltage fluctuation between the power plane 20 and the ground plane 10 or the ground bouncing during the IC circuit operations including switch operations. Particularly, for the devices having high-speed performance, the switch rate becomes sufficiently high. As a result, the voltage fluctuation becomes more and more serious. In order to alleviate the issues and to decrease the noises resulting from the voltage fluctuations, the conventional approach is to use a by-pass capacitor connecting between a power ring 40 and a ground ring 35, which are formed on the top signal layer. The capacitor was connected to the power ring 40 and ground ring 35 through via holes that connect to the power plane 20 and to the ground plane 30, respectively, so as to filter the noises and stabilize the voltages.
The capacitor assembled to the substrate requires extra-steps to pick and place, and thus increases the cycle time of process and decreases the reliability as well. However, the performance of devices on the high switch frequency operation needs a capacitor to maintain it. And for the present IC designs, especially to the PCB used in the computer field, the current in the power plane usually suffers a problem in high frequency (above than 200 MHz). Alternatively, another conventional approach proposed is to use the natural capacitance between power and ground plane. In that method, the thickness of the dielectric layer between the power plane and the ground plane is decreased if it is intended to form sufficient large capacitance. The method though solves the cycle time during assembling. However, for the thickness of the dielectric layer 25 between the power plane 20 and the ground plane 30 required special design that the process is inflexible. Besides, another group of the power plane and the ground plane will be required in order to increase the capacitance in advance.
In addition to aforementioned PCB, for the purpose of increasing the clock speed of the system and having more multi-functions in unit chip, the devices within a chip are necessary to be drastically increased. As a consequence, the number of a IC chip package leads become very huge. For example, the package of the pin grid array (PGA) has leads over 200 in repose to the demanded of great number of interconnections and the I/O requirement. Furthermore, the flip-chip build up technique and the ball grid array (BGA) etc., have been constructed recently in repose to the high speed devices and a large number of I/O leads. However, with the increasing switching rate in a chip, the noise interference becomes more and more serious than before. Therefore, the multi-layered substrate for BGA package or flip-chip package chips is necessary having noise decouple capacitors. Unfortunately, in a limited space as a build up substrate or BGA substrate, to build the capacitors are more difficult than general PCB. And thus an object of the present invention herein is to provide a high efficiency method by forming the built-in capacitors, which have more flexibility than prior art.
An object of the present invention is to provide a multi-layered substrate with built-in capacitors structure and the manufacture method thereof.
An another object of the present invention is to solve the pick and place of exterior capacitor, which is on the top signal layer.
The present invention discloses a multi-layered substrate having built-in capacitors. The structure comprises an stack-up substrate of a top signal plane/ a first dielectric layer/ a ground plane/ a second dielectric layer/ a power plane/ a third dielectric layer/ a bottom signal plane. All layers are stacked and sintered as an assembled board. The assembled board has a plurality of via holes therein to connect the wiring on each signal plane, the power plane and the ground plane. In the power plane/ the second dielectric layer/ ground plane stacked layer contains at least one desired build-in capacitor. The build-in capacitor has high permittivity of dielectric material to obtain a sufficient large capacitance. The capacitance of the built-in capacitors is easily to adjust by filling different dielectric material into the different via holes and/or combined with adjusting the dielectric layer between power plane and ground plane if it is necessary.
The method of manufacturing the built-in capacitors in multi-layered substrate proposed by the present invention is to fill a dielectric material into each of predetermined via holes in the dielectric layer between power plane and ground plane. Preferably, the dielectric material used should have a very high dielectric constant value of about two orders of magnitude larger than that of the BT core.